The last batch of Hillary Clinton emails released by the State Department included one from Clinton asking to borrow a book called “Send: Why People Email So Badly and How to Do It Better,” by David Shipley and Will Schwalbe.

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Clinton has not said why she requested the book, but it includes some advice that is particularly interesting in light of the controversy over her unconventional email arrangement at the State Department and her decision to delete tens of thousands of emails she deemed to be purely personal.

The copy that ABC downloaded for $9.99 had some interesting revelations.

Take, for example, Chapter Six: “The Email That Can Land You In Jail.” The chapter includes a section entitled “How to Delete Something So It Stays Deleted.”

“Some people are hoarders, some are checkers,” the authors write. “The main thing to consider is that once you do decide to delete, it’s like taking the garbage from your kitchen and putting it in your hallway. It’s still there.”

The chapter advised that to truly delete emails may require a special rewriting program “to make sure that it’s not just elsewhere on the drive but has in fact been written over sixteen or twenty times and rendered undefinable.”

But Shipley and Schwalbe warn that deleting emails could lead to future legal troubles.

On page 215, the authors list “Stupid (and Real) Email Phrases That Wound Up in Court.” Number one on the list? “DELETE THIS EMAIL!’ Later, on page 226, the writers warn, “If you’re issued a subpoena, your deletion binge will only make you look guilty.”

The FBI is investigating the handling of classified information in Clinton’s emails, while she maintains she has done nothing illegal or improper.

Instead of deleting, the authors suggest never putting sensitive information in an email, quoting disgraced former New York Governor Eliot Spitzer: “'Never talk when you can nod. And never write when you can talk. My only addendum is never put it in an email.' (We know…we know. Spitzer resigned. And before that, his short-lived administration was embroiled in a controversy where the smoking guns were on email. But it’s still really good advice.)”